Honestly, I'm more comfortable playing, say, Aurora and Orion, than Su Ren because the latter is a short-range character. That means she is (well at least one would think so!) harmed more often than a long-range character.

However, she has at least 2 things (that I can think off at the moment) which help her survivability:

(a) She has 2 dashes but the second dash has to be used the turn after the first one; otherwise it's wasted and the cooldown starts.

(b) The dashes and buff/debuff ability give her lots of energy while her healing can also give lots if hit multiple allies. This then hastens the time to get her ultimate, which is a good protective ability.

The build (and only one) I'm using is as follows:
(please refer to this Wikia for more details on his abilities and mods)

(1) Martial Master - Zen State (3 loadout points)

Doesn't seem to be a popular mod. I see players usually take Bo Staff Skills (get ultimate faster) or Forceful Strike (default). 3 health may look small but it does help her survivability e.g. just need to survive that turn and ultimate is up next turn, and occasionally saves her life (as evidenced by the video below).

(2) Serenity - Close to Greatness (2 loadout points)

I prefer Gaia's Blessing but there are not enough loadout points and so I stick to this default mod. This means that I can't go for clutch healing and instead should top up allies hp as often as possible, which makes this mod equally as good as Gaia's Blessing when played this way.

(3) Shifting Winds - Swift as the Wind (2 loadout points)

I know many players prefer Protector for clutch healing but I prioritise my survivability a little more. Dead support is bad for team, don't you think so? However, having said that, the reason why I switched from Protector was because the number of times my second dash was wasted was just significant enough to warrant this change.

(4) Spirit Bend - Chi Overflow (1 loadout point)

Give ally energy? Great! Spiritual Journey is better but too expensive as it would mean giving up some other mod choices. In any case, often time this ability is used only if there is nothing else better to do.

(5) Karmic Justice - Gaia's Chosen (2 loadout points)

As a friend said, this default mod gives the team a win-win situation (provided the target's not dead): if target takes damage, it gets to deal damage next turn. If target does not take damage, it gets the full healing.